1. Field of the Invention
The present invention relates to an airbag apparatus mountable on a vehicle. More particularly, the invention relates to an airbag apparatus in which a vent hole of an airbag is covered by a cover portion, which is continuous with a tether that controls a clearance between a vehicle body side wall and an occupant side wall of the airbag at inflation, and the vent hole is opened when the cover portion loosens along with loosening of the tether when the airbag cushions an occupant, and an inflation gas is exhausted from the opened vent hole.
2. Description of Related Art
JP 2012-061982 A discloses a known airbag apparatus with a vent mechanism for preventing undue elevation of airbag pressure, in which a vent hole is opened with the aid of loosening of a tether. In the airbag apparatus, an airbag is so inflatable as to separate a vehicle body side wall deployable toward a vehicle body structure and an occupant side wall deployable toward an occupant, and includes a tether that connects the vehicle body side wall and the occupant side wall for controlling a clearance between the vehicle body side wall and the occupant side wall at airbag inflation. The vent hole is formed on the part of the vehicle body side wall and a cover portion, which is formed continuously with the tether, covers the vent hole. The cover portion loosens and opens the vent hole when the occupant side wall catches an occupant and moves toward the vehicle body side wall, thereby exhausting an inflation gas.
More specifically, in the above airbag, an inner panel with an inner opening is located on an inner surface of the vehicle body side wall, at the location of the vent hole. The cover portion continuous with the tether is located between the vent hole and the inner panel. The first end of the tether on the side of the cover portion is joined to the vehicle body side wall whereas the second end of the tether away from the cover portion is joined to the occupant side wall. The inner panel covers an inner surface of the cover portion and joined to the vehicle body side wall by its opposite edges in a width direction of the cover portion. The inner opening is located at the center of the inner panel so as to allow an internal pressure of the airbag to act on the cover portion.
With this vent mechanism, when the occupant side wall catches an occupant at airbag inflation and moves toward the vehicle body side wall, the tether loosens, and the cover portion receives an internal pressure of the airbag through the inner opening of the inner panel and loosens outwardly in such a manner as to pass through the vent hole, and then slips out of a space between the inner opening and vent hole, thereby opening the vent hole. Thus an inflation gas is released from the vent hole.
However, in the conventional airbag apparatus, when the cover portion loosens and opens the vent hole, the cover portion passes through the vent hole only for the loosening amount of the only one tether extending from a part of the cover portion not joined to the vehicle body side wall.
In other words, the height of the cover portion which has slipped out of the vent hole is only half of a distance that the occupant side wall moves toward the vehicle body side wall. This is not enough to open the vent hole sufficiently and release an inflation gas quickly.